Toll-like receptor 3 expression inhibits cell invasion and migration and predicts a favorable prognosis in neuroblastoma

Toll-like receptor 3: a double-edged sword

The discovery of Toll-like receptors (TLRs) and their role in dendritic cells earned the Nobel Prize for 2011 because TLRs profoundly enhanced our understanding of the immune system. Specifically, TLR3 is located within the endosomal compartments of dendritic cells and plays a crucial role in the immune response by acting as a pattern recognition receptor that detects both exogenous (viral) and endogenous (mammalian) double-stranded RNA. However, TLR3 activation is a double-edged sword in various immune-mediated diseases. On one hand, it can enhance anti-viral defenses and promote pathogen clearance, contributing to host protection. On the other hand, excessive or dysregulated TLR3 signaling can lead to chronic inflammation and tissue damage, exacerbating conditions such as autoimmune diseases, chronic viral infections, and cancer. In cancer, TLR3 expression has been linked to both favorable and poor prognoses, though the underlying mechanisms remain unclear. Recent clinical and preclinical advances have explored the use of TLR3 agonists in cancer immunotherapy, attempting to capitalize on their potential to enhance anti-tumor responses. The dual role of TLR3 highlights its complexity as a therapeutic target, necessitating careful modulation to maximize its protective effects while minimizing potential pathological consequences. In this review, we explore the intricate roles of TLR3 in immune responses across different disease contexts, including cancer, infections, autoimmune disorders, and allergies, highlighting both its protective and detrimental effects in these disorders, as well as progress in developing TLR3 agonists as part of the immunotherapy landscape.

An anoikis-related signature predicts prognosis and immunotherapy response in gastrointestinal cancers

Background

Gastrointestinal (GI) cancers have high incidence rates and mortality rates. Anoikis is a special type of cell apoptosis, and anoikis resistance has been reported to be associated with tumor malignancy. We aimed to explore the roles of anoikis-related genes (ARGs) in the GI cancer prognosis.

Methods

We extracted RNA sequencing and clinical data from The Cancer Genome Atlas and Gene Expression Omnibu databases for patients with esophageal cancer, gastric cancer, colon cancer and rectal cancer and identified ARGs from GeneCards and Harmonizome. Anoikis-related patterns were identified via unsupervised clustering analysis. We constructed a prognostic signature (Anoscore) based on prognostic ARGs through univariate, LASSO, and multivariate Cox regression analyses. The model was validated and evaluated using Kaplan-Meier analysis, receiver operating characteristic curves, univariate Cox regression analysis, multivariate Cox regression analysis, column charts, and calibration curves. We also performed a single-cell sequencing analysis of candidate genes via TISCH2. A correlation analysis between the Anoscore, the tumor microenvironment and drug sensitivity was conducted in GI cancers. The expression and function of some candidate genes were validated in vitro.

Results

In terms of prognostic ARGs, two anoikis-related patterns, ARG clusters A and B, were identified. ARG cluster B had a worse prognosis than did ARG cluster A. Subsequently, the Anoscore was developed as an independent prognostic factor. It demonstrated the robust predictive capability for the prognosis of patients with GI cancers. Notably, patients with high Anoscores exhibited poor outcomes. In addition, we established a nomogram (Ano-nomogram) based on the Anoscore and clinicopathological factors of patients to predict the 3-year and 5-year survival probabilities. Moreover, patients with high Anoscores had higher levels of immune cell infiltration and higher immune checkpoint expression. The drug sensitivity analysis revealed that patients with high or low Anoscores were sensitive to different chemotherapies and targeted drugs. S100A11 and TLR3, representative candidate genes, exhibited different expression patterns and biological functions.

Conclusion

This study highlighted the significant potential of the Anoscore in predicting prognosis and guiding the selection of personalized therapeutic regimens for patients with GI cancers.

Toll-Like Receptors and the Response to Radiotherapy in Solid Tumors: Challenges and Opportunities

Toll-like receptors (TLRs) are indispensable for the activation, maintenance and halting of immune responses. TLRs can mediate inflammation by recognizing molecular patterns in microbes (pathogen-associated molecular patterns: PAMPs) and endogenous ligands (danger-associated molecular patterns: DAMPs) released by injured or dead cells. For this reason, TLR ligands have attracted much attention in recent years in many cancer vaccines, alone or in combination with immunotherapy, chemotherapy and radiotherapy (RT). TLRs have been shown to play controversial roles in cancer, depending on various factors that can mediate tumor progression or apoptosis. Several TLR agonists have reached clinical trials and are being evaluated in combination with standard of care therapies, including RT. Despite their prolific and central role in mediating immune responses, the role of TLRs in cancer, particularly in response to radiation, remains poorly understood. Radiation is recognized as either a direct stimulant of TLR pathways, or indirectly through the damage it causes to target cells that subsequently activate TLRs. These effects can mediate pro-tumoral and anti-tumoral effects depending on various factors such as radiation dose and fractionation, as well as host genomic features. In this review, we examine how TLR signaling affects tumor response to RT, and we provide a framework for the design of TLR-based therapies with RT.

Epigenetic state determines inflammatory sensing in neuroblastoma

Immunotherapy has revolutionized cancer treatment, but many cancers are not impacted by currently available immunotherapeutic strategies. Here, we investigated inflammatory signaling pathways in neuroblastoma, a classically "cold" pediatric cancer. By testing the functional response of a panel of 20 diverse neuroblastoma cell lines to three different inflammatory stimuli, we found that all cell lines have intact interferon signaling, and all but one lack functional cytosolic DNA sensing via cGAS-STING. However, double-stranded RNA (dsRNA) sensing via Toll-like receptor 3 (TLR3) was heterogeneous, as was signaling through other dsRNA sensors and TLRs more broadly. Seven cell lines showed robust response to dsRNA, six of which are in the mesenchymal epigenetic state, while all unresponsive cell lines are in the adrenergic state. Genetically switching adrenergic cell lines toward the mesenchymal state fully restored responsiveness. In responsive cells, dsRNA sensing results in the secretion of proinflammatory cytokines, enrichment of inflammatory transcriptomic signatures, and increased tumor killing by T cells in vitro. Using single-cell RNA sequencing data, we show that human neuroblastoma cells with stronger mesenchymal signatures have a higher basal inflammatory state, demonstrating intratumoral heterogeneity in inflammatory signaling that has significant implications for immunotherapeutic strategies in this aggressive childhood cancer.

Toll-like receptor 3 is a potential prognosis marker and associated with immune infiltration in stomach adenocarcinoma

BACKGROUND

Toll-like receptors participate in various biological mechanisms, mainly including the immune response and inflammatory response. Nevertheless, the role of TLRs in STAD remains unclear.

OBJECTIVE

We aimed to explore the expression, prognosis performance of TLRs in STAD and their relationship with immune infiltration.

METHODS

Student's t-test was used to evaluate the expression of TLRs between STAD tissues and normal tissues. Kaplan-Meier method was applied to explored the prognosis value of TLRs in STAD. And qRT-PCR validated their expression and prognosis value. Spearman's correlation analysis and Wilcoxon rank-sum test were used to assess the association between TLRs and immune infiltration in STAD.

RESULTS

The mRNA level of TLR3 was downregulated in STAD. We summarized genetic mutations and CNV alteration of TLRs in STAD cohort. Prognosis analysis revealed that STAD patients with high TLR3 expression showed better prognosis in OS, FP and PPS. The result of qRT-PCR suggested that TLR3 expression was decreased in STAD tissues and STAD patients with high TLR3 mRNA level had a better OS. Univariate and multivariate cox regression analysis suggested TLR3 expression and clinical stage as independent factors affecting STAD patients' prognosis. A positive association existed between TLR3 expression and the abundance of immune cells and the expression of various immune biomarkers. Furthermore, key targets related to TLR3 were identified in STAD, mainly including MIR-129 (GCAAAAA), PLK1, and V$IRF1_01.

CONCLUSIONS

Our result demonstrated TLR3 as a prognosis marker and associated with immune infiltration in STAD.

Methylation Regulation of TLR3 on Immune Parameters in Lung Adenocarcinoma

This study aims to analyze the methylation regulation of TLR3 in lung adenocarcinoma (LUAD) and to explore the association of TLR3 expression with immune microenvironment. TLR3 has a decreased expression in LUAD tissues and low expression of TLR3 is not only associated with poor prognosis in patients with LUAD, but also can be used as a diagnostic marker. Bisulfite sequencing PCR (BSP) results showed that the methylation level in the promoter of TLR3 was negatively correlated with the level of TLR3 mRNA in LUAD tissues. TIMER analysis showed that TLR3 was negatively correlated with the tumor purity of LUAD and positively with immune cell infiltration to some extent. ESTIMATE analysis also suggested that TLR3 expression and its methylation had significant correlation with immune score. The lower immune scores were associated with the late stage of LUAD and poor prognosis. The high expression of TLR3 might inhibit the development of LUAD by activating apoptosis pathway. The proteins interacted with TLR3 were mainly involved in the apoptosis pathway and positively correlated with the key genes (MYD88, Caspase 8, BIRC3, PIK3R1) in this pathway. Therefore, TLR3 as a key biomarker for prognosis and diagnosis in LUAD, might be considered as a potential epigenetic and immunotherapeutic target.

Roles of Toll-Like Receptor 3 in Human Tumors

Toll-like receptor 3 (TLR3) is an important member of the TLR family, which is an important group of pathogen-associated molecular patterns. TLR3 can recognize double-stranded RNA and induce activation of NF-κB and the production of type I interferons. In addition to its immune-associated role, TLR3 has also been detected in some tumors. However TLR3 can play protumor or antitumor roles in different tumors or cell lines. Here, we review the basic signaling associated with TLR3 and the pro- or antitumor roles of TLR3 in different types of tumors and discuss the possible reasons for the opposing roles of TLR3 in tumors.

Receptor-interacting protein kinase 1 is a key mediator in TLR3 ligand and Smac mimetic-induced cell death and suppresses TLR3 ligand-promoted invasion in cholangiocarcinoma

BACKGROUND

Toll-like receptor 3 (TLR3) ligand which activates TLR3 signaling induces both cancer cell death and activates anti-tumor immunity. However, TLR3 signaling can also harbor pro-tumorigenic consequences. Therefore, we examined the status of TLR3 in cholangiocarcinoma (CCA) cases to better understand TLR3 signaling and explore the potential therapeutic target in CCA.

METHODS

The expression of TLR3 and receptor-interacting protein kinase 1 (RIPK1) in primary CCA tissues was assayed by Immunohistochemical staining and their associations with clinicopathological characteristics and survival data were evaluated. The effects of TLR3 ligand, Poly(I:C) and Smac mimetic, an IAP antagonist on CCA cell death and invasion were determined by cell death detection methods and Transwell invasion assay, respectively. Both genetic and pharmacological inhibition of RIPK1, RIPK3 and MLKL and inhibitors targeting NF-κB and MAPK signaling were used to investigate the underlying mechanisms.

RESULTS

TLR3 was significantly higher expressed in tumor than adjacent normal tissues. We demonstrated in a panel of CCA cell lines that TLR3 was frequently expressed in CCA cell lines, but was not detected in a nontumor cholangiocyte. Subsequent in vitro study demonstrated that Poly(I:C) specifically induced CCA cell death, but only when cIAPs were removed by Smac mimetic. Cell death was also switched from apoptosis to necroptosis when caspases were inhibited in CCA cells-expressing RIPK3. In addition, RIPK1 was required for Poly(I:C) and Smac mimetic-induced apoptosis and necroptosis. Of particular interest, high TLR3 or low RIPK1 status in CCA patients was associated with more invasiveness. In vitro invasion demonstrated that Poly(I:C)-induced invasion through NF-κB and MAPK signaling. Furthermore, the loss of RIPK1 enhanced Poly(I:C)-induced invasion and ERK activation in vitro. Smac mimetic also reversed Poly(I:C)-induced invasion, partly mediated by RIPK1. Finally, a subgroup of patients with high TLR3 and high RIPK1 had a trend toward longer disease-free survival (p = 0.078, 28.0 months and 10.9 months).

CONCLUSION

RIPK1 plays a pivotal role in TLR3 ligand, Poly(I:C)-induced cell death when cIAPs activity was inhibited and loss of RIPK1 enhanced Poly(I:C)-induced invasion which was partially reversed by Smac mimetic. Our results suggested that TLR3 ligand in combination with Smac mimetic could provide therapeutic benefits to the patients with CCA. Video abstract.

Trial watch: TLR3 agonists in cancer therapy

Toll-like receptor 3 (TLR3) is a pattern recognition receptor that senses exogenous (viral) as well as endogenous (mammalian) double-stranded RNA in endosomes. On activation, TLR3 initiates a signal transduction pathway that culminates with the secretion of pro-inflammatory cytokines including type I interferon (IFN). The latter is essential not only for innate immune responses to infection but also for the initiation of antigen-specific immunity against viruses and malignant cells. These aspects of TLR3 biology have supported the development of various agonists for use as stand-alone agents or combined with other therapeutic modalities in cancer patients. Here, we review recent preclinical and clinical advances in the development of TLR3 agonists for oncological disorders.

Abbreviations

cDC, conventional dendritic cell; CMT, cytokine modulating treatment; CRC, colorectal carcinoma; CTL, cytotoxic T lymphocyte; DC, dendritic cell; dsRNA, double-stranded RNA; FLT3LG, fms-related receptor tyrosine kinase 3 ligand; HNSCC, head and neck squamous cell carcinoma; IFN, interferon; IL, interleukin; ISV, in situ vaccine; MUC1, mucin 1, cell surface associated; PD-1, programmed cell death 1; PD-L1, programmed death-ligand 1; polyA:U, polyadenylic:polyuridylic acid; polyI:C, polyriboinosinic:polyribocytidylic acid; TLR, Toll-like receptor.

Immunogenic Cell Death Driven by Radiation-Impact on the Tumor Microenvironment

Immunogenic cell death (ICD) is a particular form of cell death that can initiate adaptive immunity against antigens expressed by dying cells in the absence of exogenous adjuvants. This implies that cells undergoing ICD not only express antigens that are not covered by thymic tolerance, but also deliver adjuvant-like signals that enable the recruitment and maturation of antigen-presenting cells toward an immunostimulatory phenotype, culminating with robust cross-priming of antigen-specific CD8⁺ T cells. Such damage-associated molecular patterns (DAMPs), which encompass cellular proteins, small metabolites and cytokines, are emitted in a spatiotemporally defined manner in the context of failing adaptation to stress. Radiation therapy (RT) is a bona fide inducer of ICD, at least when employed according to specific doses and fractionation schedules. Here, we discuss the mechanisms whereby DAMPs emitted by cancer cells undergoing RT-driven ICD alter the functional configuration of the tumor microenvironment.

Toll-like receptor 3 as a new marker to detect high risk early stage Non-Small-Cell Lung Cancer patients

Immune and epithelial cells express TLR3, a receptor deputed to respond to microbial signals activating the immune response. The prognostic value of TLR3 in cancer is debated and no data are currently available in NSCLC, for which therapeutic approaches that target the immune system are providing encouraging results. Dissecting the lung immune microenvironment could provide new prognostic markers, especially for early stage NSCLC for which surgery is the only treatment option. In this study we investigated the expression and the prognostic value of TLR3 on both tumor and immune compartments of stage I NSCLCs. In a cohort of 194 NSCLC stage I, TLR3 immunohistochemistry expression on tumor cells predicted a favorable outcome of early stage NSCLC, whereas on the immune cells infiltrating the tumor stroma, TLR3 expression associated with a poor overall survival. Patients with TLR3-positive immune infiltrating cells, but not tumor cells showed a worse prognosis compared with all other patients. The majority of TLR3-expressing immune cells resulted to be macrophages and TLR3 expression associates with PD-1 expression. TLR3 has an opposite prognostic significance when expressed on tumor or immune cells in early stage NCSCL. Analysis of TLR3 in tumor and immune cells can help in identifying high risk stage I patients for which adjuvant treatment would be beneficial.

Therapeutic Cancer Vaccines-T Cell Responses and Epigenetic Modulation

There is great interest in developing efficient therapeutic cancer vaccines, as this type of therapy allows targeted killing of tumor cells as well as long-lasting immune protection. High levels of tumor-infiltrating CD8⁺ T cells are associated with better prognosis in many cancers, and it is expected that new generation vaccines will induce effective production of these cells. Epigenetic mechanisms can promote changes in host immune responses, as well as mediate immune evasion by cancer cells. Here, we focus on epigenetic modifications involved in both vaccine-adjuvant-generated T cell immunity and cancer immune escape mechanisms. We propose that vaccine-adjuvant systems may be utilized to induce beneficial epigenetic modifications and discuss how epigenetic interventions could improve vaccine-based therapies. Additionally, we speculate on how, given the unique nature of individual epigenetic landscapes, epigenetic mapping of cancer progression and specific subsequent immune responses, could be harnessed to tailor therapeutic vaccines to each patient.

Innate immune sensor laboratory of genetics and physiology 2 suppresses tumor cell growth and functions as a prognostic marker in neuroblastoma

The innate immune receptors, such as toll-like receptor 3 (TLR3), melanoma differentiation-associated 5 (MDA5) and retinoic acid-inducible gene-I (RIG-I), have been shown to be differentially expressed in neuroblastoma (NB) and promote dsRNA poly (I:C)-induced NB suppression in vitro and in vivo. However, the role of another important innate immune cytosolic sensor, laboratory of genetics and physiology 2 (LGP2), in the cancer behavior of NB remains unclear. Here, we demonstrated that the expression levels of LGP2 were either low or undetectable in all NB cell lines tested with or without MYCN amplification. LGP2 expression levels were significantly increased only in NB cells without MYCN amplification, including SK-N-AS and SK-N-FI after poly (I:C) treatment in vitro and in mouse xenograft models. Ectopic expression of LGP2 in NB cells significantly enhanced poly (I:C)-induced NB cell death associated with downregulation of MDA5, RIG-I, MAVS and Bcl-2, as well as upregulation of Noxa and tBid. By immunofluorescence analyses, LGP2 localized mainly in the cytoplasm of NB cells after poly (I:C) treatment. In human NB tissue samples, cytoplasmic LGP2 expression was positively correlated with histological differentiation and inversely correlated with MYCN amplification. Positive cytoplasmic LGP2 expression in tumor tissues could predict a favorable outcome in NB patients independent of other prognostic factors. In short, LGP2 was effective in promoting poly (I:C)-induced NB suppression and cytoplasmic LGP2 can serve as an independent favorable prognostic factor in NB patients.

Combinatorial treatment with polyI:C and anti-IL6 enhances apoptosis and suppresses metastasis of lung cancer cells

Activation of TLR3 stimulates cancer cell apoptosis and triggers secretion of inflammatory cytokines. PolyI:C, a TLR3 agonist, activates immune cells and regresses metastatic lung cancer in vivo. Although polyI:C reportedly kills lung carcinomas, the mechanism remains elusive. Here, we demonstrated that polyI:C suppressed the proliferation and survival of metastatic (NCI-H358 and NCI-H292) and non-metastatic (A549) lung cancer cells. Notably, A549, NCI-H292 and NCI-H358 which are inducible by polyI:C, expressed low-to-medium level of TLR3 protein, and were susceptible to polyI:C treatment. By contrast, NCI-H1299, which endogenously expresses high level of TLR3 protein, was insensitive to polyI:C. We showed that polyI:C stimulated pro-inflammatory cytokines associated with survival and metastasis in a cell type-specific manner. While A549 and NCI-H292 released high levels of IL6, IL8 and GRO, the NCI-H358 cells endogenously secretes abundant levels of these cytokines, and was not further induced by polyI:C. Thus, NCI-H358 was resistant to the inhibition of cytokine-dependent metastasis. NCI-H1299, which was unresponsive to polyI:C, did not produce any of the pro-inflammatory cytokines. Treatment of A549 with a combination of polyI:C and anti-IL6 antibody significantly decreased IL6 production, and enhanced polyI:C-mediated killing and suppression of oncogenicity and metastasis. While polyI:C stimulated the phosphorylation of STAT3 and JAK2, blockade of these proteins enhanced polyI:C-mediated suppression of survival and metastasis. Taken together, polyI:C alone provoked apoptosis of lung cancer cells that express low-to-medium levels of functional TLR3 protein. The combinatorial treatment with polyI:C and anti-IL6 enhanced polyI:C-mediated anticancer activities through IL6/JAK2/STAT3 signalling, and apoptosis via TLR3-mediated caspase 3/8 pathway.

TLR3 expression status predicts prognosis in patients with advanced thoracic esophageal squamous cell carcinoma after esophagectomy

BACKGROUND

The relationship between Toll-like receptors (TLRs) and esophageal squamous cell carcinoma (ESCC) is not completely understood.

METHODS

RT-qPCR was used to evaluate the mRNA expression of TLR1-10 in 13 ESCC lines. We then used ESCC tissue microarray (TMA) to confirm expression of TLR3 protein in patients with ESCC.

RESULTS

All ESCC lines showed 10-60 times higher TLR3 mRNA expression than PBLs. High expression of TLR3 correlated with favorable 5-year overall survival (OS) and disease specific survival (DSS) among patients with ESCC after esophagectomy (p < 0.01). Additionally, In the adjuvant chemotherapy group, TLR3 high patients had significantly better 5-year OS compared to TLR3 low patients (60.2%, 34.4%, respectively) but not in the surgery alone group.

CONCLUSION

High TLR3 expression is an independent prognostic factor and has the potential to serve as a clinically useful marker of the need for adjuvant chemotherapy after esophagectomy in patients with advanced thoracic ESCC.

PD-L1, inflammation, non-coding RNAs, and neuroblastoma: Immuno-oncology perspective

Neuroblastoma is the most common pediatric solid tumor of neural crest origin. The current treatment options for neuroblastoma produce severe side effects. Programmed death-ligand 1 (PD-L1), chronic inflammation, and non-coding RNAs are known to play a significant role in the pathogenesis of neuroblastoma. Cancer cells and the surrounding cells in the tumor microenvironment express PD-L1. Programmed death-1 (PD-1) is a co-receptor expressed predominantly by T cells. The binding of PD-1 to its ligands, PD-L1 or PD-L2, is vital for the physiologic regulation of the immune system. Chronic inflammation is involved in the recruitment of leukocytes, production of cytokines and chemokines that in turn, lead to survival, metastasis, and angiogenesis in neuroblastoma tumors. The miRNAs and long non-coding (lnc) RNAs have emerged as a novel class of non-coding RNAs that can regulate neuroblastoma associated cell-signaling pathways. The dysregulation of PD-1/PD-L1, inflammatory pathways, lncRNAs, and miRNAs have been reported in clinical and experimental samples of neuroblastoma. These signaling molecules are currently being evaluated for their potential as the biomarker and therapeutic targets in the management of neuroblastoma. A monoclonal antibody called dinutuximab (Unituxin) that attaches to a carbohydrate molecule GD2, on the surface of many neuroblastoma cells, is being used as an immunotherapy drug for neuroblastoma treatment. Atezolizumab (Tecentriq), an engineered monoclonal antibody against PD-L1, are currently in clinical trial for neuroblastoma patients. The lncRNA/miRNA-based therapeutics is being developed to deliver tumor suppressor lncRNAs/miRNAs or silencing of oncogenic lncRNAs/miRNAs. The focus of this review is to discuss the current knowledge on the immune checkpoint molecules, PD-1/PD-L1 signaling, inflammation, and non-coding RNAs in neuroblastoma.

Exploiting poly(I:C) to induce cancer cell apoptosis

TLR3 belong to the Toll-like receptors family, it is mainly expressed on immune cells where it senses pathogen-associated molecular patterns and initiates innate immune response. TLR3 agonist poly(I:C) was developed to mimic pathogens infection and boost immune system activation to promote anti-cancer therapy. Accordingly, TLR agonists were included in the National Cancer Institute list of immunotherapeutic agents with the highest potential to cure cancer. Besides well known effects on immune cells, poly(I:C) was also shown, in experimental models, to directly induce apoptosis in cancer cells expressing TLR3.

This review presents the current knowledge on the mechanism of poly(I:C)-induced apoptosis in cancer cells. Experimental evidences on positive or negative regulators of TLR3-mediated apoptosis induced by poly(I:C) are reported and strategies are proposed to successfully promote this event in cancer cells.

Cancer cells apoptosis is an additional arm offered by poly(I:C), besides activation of immune system, for the treatment of various type of cancer. A further dissection of TLR3 signaling would contribute to greater resolution of the critical steps that impede full exploitation of the poly(I:C)-induced apoptosis. Experimental evidences about negative regulator of poly(I:C)-induced apoptotic program should be considered in combinations with TLR3 agonists in clinical trials.

Downregulation of c-Myc is involved in TLR3-mediated tumor death of neuroblastoma xenografts

Neuroblastoma (NB) is the deadliest pediatric solid tumor due to its pleomorphic molecular characteristics. In the innate immune system, toll-like receptor 3 (TLR3) recognizes viral double-stranded RNAs to initiate immune signaling. Positive TLR3 expression indicates a favorable prognosis in NB patients, and is associated with MYCN-non-amplified. However, TLR3-mediated innate immune responses remain elusive in NB. In this study, we attempted to dissect the molecular mechanism underlying TLR3-agonist polyinosinic-polycytidylic acid [poly(I:C)] treatment in NB in vivo. We established NB xenograft models in non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice with MYCN-amplified SK-N-DZ (DZ) cells or MYCN-non-amplified SK-N-AS (AS) cells. Poly(I:C) treatment led to significant tumor regression in AS xenografts, but not in DZ xenografts. Through immunohistochemical analysis, significant suppression of tumor proliferation, downregulation of c-Myc expression, and upregulation of TLR3 expression were found in the treatment group. Poly(I:C) inducing activation of TLR3/IRF3-mediated innate immunity associated with downregulation of c-Myc can be found in MYCN-non-amplified SK-N-AS cells, but not in MYCN-amplified BE(2)-M17 cells. Knockdown of TLR3 disturbed poly(I:C)-induced suppression of c-Myc and upregulation of p-IRF3 in AS cells. Furthermore, poly(I:C) treatment upregulated active NF-κB, mitochondrial antioxidant manganese superoxide dismutase and 8-hydroxydeoxyguanosine, which works with reactive oxygen species (ROS) generation and DNA damage. Upregulation of active caspase 3 and cleaved poly [ADP-ribose] polymerase 1 were found in poly(I:C)-treated AS xenografts, which indicates the induction of apoptosis. Thus, our results suggest that c-Myc overexpression may increase sensitivity to poly(I:C)-induced tumor growth arrest and ROS-mediated apoptosis in NB. This study demonstrates that c-Myc protein expression has an important role in TLR3-induced innate immune responses, providing future treatment recommendations.

Innate immune signaling through differential RIPK1 expression promote tumor progression in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a devastating disease for which new treatments, such as immunotherapy are needed. Synthetic double-stranded RNAs, which activate toll-like receptor 3 (TLR3), have been used as potent adjuvants in cancer immunotherapy by triggering a proapoptotic response in cancer cells. A better understanding of the mechanism of TLR3-mediated apoptosis and its potential involvement in controlling tumor metastasis could lead to improvements in current treatment. Using paired, autologous primary and metastatic HNSCC cells we previously showed that metastatic, but not primary tumor-derived cells, were unable to activate prosurvival NF-κB in response to p(I):p(C) resulting in an enhanced apoptotic response. Here, we show that transcriptional downregulation of receptor-interacting serine/threonine-protein kinase 1 (RIPK1) in metastatic HNSCC cells causes a loss of TLR3-mediated NF-κB signaling, resulting in enhanced apoptosis. Loss of RIPK1 strongly correlates with metastatic disease in a cohort of HNSCC patients. This downregulation of RIPK1 is possibly mediated by enhanced methylation of the RIPK1 promoter in tumor cells and enhances protumorigenic properties such as cell migration. The results described here establish a novel mechanism of TLR3-mediated apoptosis in metastatic cells and may create new opportunities for using double stranded RNA to target metastatic tumor cells.

MDA5 complements TLR3 in suppression of neuroblastoma

Toll-like receptor3 (TLR3) has been confirmed to be differentially expressed in neuroblastoma (NB), and predicts a favorable prognosis with a high expression in tumor tissues. Treatment with TLR3 agonist--polyinosinic-polycytidylic acid [poly(I:C)] could induce significant but limited apoptosis in TLR3-expressing NB cells, suggesting that other viral RNA sensors, including melanoma differentiation-associated gene 5 (MDA5) and retinoic acid-inducible gene-I (RIG-I) in the cytosolic compartment might also be implicated in poly(I:C)-induced NB cell death. MDA5 and RIG-I were induced by poly(I:C) to express in two of six NB cell lines, SK-N-AS (AS) and SK-N-FI, which were associated with up-regulation of caspase9 and active caspase3. While knockdown of either MDA5 or RIG-I alone is ineffective to decrease caspase9 and active caspase3, simultaneously targeting MDA5 and TLR3 showed the best effect to rescue poly(I:C) induced up-regulation of mitochondrial antiviral signaling protein (MAVS), caspase9, active caspase3, and apoptosis in AS cells. Over-expression of MDA5 in FaDu cells resulted in significantly less colony formation and more poly(I:C)-induced cell death. Further studies in human NB tissue samples revealed that MDA5 expression in NB tissues predicted a favorable prognosis synergistically with TLR3. Our findings indicate that MDA5 may serve as a complementary role in the TLR3 activated suppression of NB.

Prognostic and Predictive Value of DAMPs and DAMP-Associated Processes in Cancer

It is now clear that human neoplasms form, progress, and respond to therapy in the context of an intimate crosstalk with the host immune system. In particular, accumulating evidence demonstrates that the efficacy of most, if not all, chemo- and radiotherapeutic agents commonly employed in the clinic critically depends on the (re)activation of tumor-targeting immune responses. One of the mechanisms whereby conventional chemotherapeutics, targeted anticancer agents, and radiotherapy can provoke a therapeutically relevant, adaptive immune response against malignant cells is commonly known as “immunogenic cell death.” Importantly, dying cancer cells are perceived as immunogenic only when they emit a set of immunostimulatory signals upon the activation of intracellular stress response pathways. The emission of these signals, which are generally referred to as “damage-associated molecular patterns” (DAMPs), may therefore predict whether patients will respond to chemotherapy or not, at least in some settings. Here, we review clinical data indicating that DAMPs and DAMP-associated stress responses might have prognostic or predictive value for cancer patients.

Toll-like receptor 3 regulates NK cell responses to cytokines and controls experimental metastasis

The Toll-like receptor 3 (TLR3) agonist poly(I:C) is a promising adjuvant for cancer vaccines due to its induction of potent antitumor responses occurring primarily through the activation of dendritic cells (DCs) and natural killer (NK) cells. However, little is known about the role of TLR3 sensing of endogenous ligands in innate tumor immunosurveillance. Here, we investigated whether TLR3 could modulate immune responses and facilitate tumor control without administration of an agonist. We observed only limited impact of TLR3 deficiency on spontaneous carcinogenesis and primary growth of B16F10, E0771 or MC38 tumors when injected subcutaneously to mice. Nevertheless, TLR3 was observed to limit experimental B16F10 lung metastasis, an immunologic constraint dependent on both IFNγ secretion and NK cells. Interestingly, we observed that NK cells derived from Tlr3 null (Tlr3^-/- ) mice were hyporesponsive to cytokine stimulation. Indeed, compared with NK cells with intact TLR3, Tlr3^-/- NK cells produced significantly reduced pro-inflammatory cytokines, including IFNγ, when incubated in the presence of different combinations of IL-12, IL-18 and IL-15. Bone-marrow chimera experiments established that competent NK cell responses required TLR3 sensing on radio-sensitive immune cells. Intriguingly, although CD8α DCs robustly express high levels of TLR3, we found that those cells were not necessary for efficient IFNγ production by NK cells. Moreover, the defective NK cell phenotype of Tlr3^-/- mice appeared to be independent of the gut microbiota. Altogether, our data demonstrate a pivotal role of endogenous TLR3 stimulation for the acquisition of full NK cell functions and immune protection against experimental metastasis.

TLR3 triggering regulates PD-L1 (CD274) expression in human neuroblastoma cells

Neuroblastoma is the most common extracranial solid tumor in children, causing 12% of all pediatric cancer mortality. Neuroblastoma specific T-cells have been detected in patients, but usually fail to attack and eradicate the tumors. Tumor immune evasion may thus play an important role in neuroblastoma pathogenicity. Recent research in adult cancer patients shows that targeting T-cell check-point molecules PD-1/PD-L1 (or CD279/CD274) may bolster immune reactivity against solid tumors. Also, infections can be associated with spontaneous neuroblastoma regression. In our current study, we therefore investigated if antibody targeting of PD-L1 and triggering of selective pathogen-receptor Toll-like receptors (TLRs) potentiates immunogenicity of neuroblastoma cells. We find this to be the case. TLR3 triggering induced strong upregulation of both MHC class I and PD-L1 on neuroblastoma cells. At the same time TGF-β levels decreased and IL-8 secretion was induced. The combined neuroblastoma cell treatment using PD-L1 blockade and TLR3 triggering using virus analog poly(I:C) moreover induced CD4(+) and CD8(+) T-cell activation. Thus, we propose combined treatment using PD-L1 blockade with synthetic TLR ligands as an avenue toward new immunotherapy against human neuroblastoma.

Activation of Toll-like receptor 3 reduces actin polymerization and adhesion molecule expression in endometrial cells, a potential mechanism for viral-induced implantation failure

STUDY QUESTION

Does activation of endometrial Toll-like receptor 3 (TLR 3) affect cell receptivity to trophoblast adhesion?

SUMMARY ANSWER

TLR 3 activation in vitro reduces the attachment of trophoblast cells to endometrial cells by altering the cell cytoskeleton and reducing the expression of adhesion molecules in human endometrial cells.

WHAT IS KNOWN ALREADY

It is well documented that the presence of an infection at the time of implantation can lead to implantation failure. The female reproductive tract recognizes invading micro-organisms through the innate pathogen recognition receptors such as the TLRs.

STUDY DESIGN, SIZE, DURATION

Poly I:C was used as a TLR 3-specific ligand and endometrial cells were either treated or not with Poly I:C (treated versus control) in vitro. The experiments were performed in three replicates on three separate days.

PARTICIPANTS/MATERIALS, SETTING, METHODS

An in vitro assay was developed using RL95-2 (a human endometrial cell line) and JAr (a human trophoblast cell line) cells. Initially, the percentage of attached JAr spheroids to RL95-2 was measured in response to TLR 3 activation. Next, actin polymerization in RL95-2 cells was assessed in response to TLR 2/6, 3 and 5 activation. Phalloidin was used to assess the mean fluorescence intensity of F-actin by flow cytometry or confocal microscopy. Secondly, the influence of TLR 2/6, 3 and 5 activation on the expression of cluster of differentiation 98 (CD98) and β3 integrin was determined. To further understand through which pathways the TLR 3-induced alterations occur, inhibitors were applied for Toll/interleukin-1 receptor domain-containing adaptor inducing interferon-beta (TRIF), myeloid differentiation primary response 88 (MYD88), mitogen-activated protein kinases (MAPK) and nuclear factor pathways.

MAIN RESULTS AND THE ROLE OF CHANCE

We observed that stimulation of TLR 3 in endometrial cells with different concentrations of Poly I:C led to a reduction in the percentage of trophoblasts attached to the endometrial cells in a dose-dependent manner (P < 0.05). This decrease was consistent in the Poly I:C treated group regardless of the co-incubation time (P < 0.05). In addition, our results demonstrated that actin polymerization and CD98 expression significantly decreased only in response to TLR 3 activation (P < 0.05). Activation of endometrial cells with TLR 2/6, 3 and 5 significantly reduced β3 integrin expression (P < 0.05). These alterations were shown to work via MYD88-MAPK pathways (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

This study has been performed in vitro. Future in vivo studies will be required in order to confirm our data.

WIDER IMPLICATIONS OF THE FINDINGS

This is a novel discovery which extends our current knowledge concerning diagnosis and treatment of viral-induced infertility cases.

STUDY FUNDING/COMPETING INTERESTS

This research was supported by the COST Action FA1201 (GEMINI) by granting a Short Term Scientific Mission and the Instituto de Salud Carlos III by granting Grant PI11/01645. The authors have no conflict of interest to declare.